The invention proceeds from a planar filter The article entitled "Parallel-Coupled Transmission-Line-Resonator Filters" in the IRE Trans. on Microwave Theory and Techniques, 1958, pages 223 ff. by S. B. Cohn discloses a microstripline filter in which a plurality of striplines are arranged next to one another. In this case, the striplines overlap one another on a portion of their length and are thereby coupled to their respective neighbor. In addition, the article entitled "Filters with Single Transmission Zeros at Real or Imaginary Frequencies" in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-24, No. 4, April 1976, pages 172-181 discloses waveguide filters in which pole points are generated in the damping by overcoupling of modes between nonadjacent resonators by means of slotted diaphragms.